The present invention relates to improvements in wood screws.
As shown in FIG. 3, a conventional wood screw has a head (a) for receiving a fastening tool, a shank (b) extending from the head and including a parallel shank portion (b1) and a tapering tip (b2) formed at the tip of the parallel shank portion (b1), and a screw thread (c) formed on the tapering tip (b2) and the parallel shank portion (b1).
A screw of the so-called self-drilling type provided at the tip thereof with drilling blades (b3) as shown in FIG. 4, can also be used as a wood screw.
A wood screw may be screwed directly into an article to be fastened such as timber without boring a hole before driving. Such a mode of use presents the disadvantages that the turning torque required for fastening becomes great and the article to be fastened such as timber may be cracked.
From the study the inventor has made of such problems, it has become apparent that such problems were caused by defective discharge of chips produced at a time when a hole was bored by the tapering tip or the drilling portion. In particular, it has been found that such chips stuck to the surfaces of the screw thread and the shank near the shank tip, and in particular, in the vicinity of the tip of the parallel shank portion. In other words, chips stuck at that portion of the shank which is located slightly at the base side with respect to the tapering tip or the drilling portion. Such sticking of chips is caused by the fact that, during fastening, chips enter and are compressed between the wall of a hole bored by the tapering tip or the drilling portion and the tip end of the parallel shank portion.